240 smithsonian miscellaneous collections vol. 75 



Chancellor Formation. Allan, 1914 



Type locality. — East and north slopes of Chancellor Peak, on the 

 southwest side of the Ottertail Range. 



Derivation of name. — From Chancellor Peak. 

 Character. — (After Allan.) 



The formation is characterized throughout its thickness by its remarkable 

 lithological uniformity and by the reddish colour of the weathered outcrops 

 of its upper portion. In general the unaltered portion of the series of beds is 

 thin-bedded with a slaty cleavage parallel with the stratification plane. 



The lower members of the formation are greyish, calcareous shales, meta- 

 argillites and argillites, sometimes even phyllitic in character towards the bottom 

 of the section, weathering greenish, greyish, reddish, yellowish, and buff.* 



A characteristic feature of these rocks is their banded character as developed 

 on weathered surfaces. A rock may be dark grey on the fresh surface, but 

 where weathered it appears to be composed of bands of grey, alternating with 

 others of red, yellow, or brown colour. In other examples the fresh rock 

 may be a blue limestone or calcareous slate, and yet where weathered it shows 

 a distinct banding due to alternating bluish and buff coloured layers, or bluish 

 and yellowish layers. Again, as it frequently happens, certain bands resist the 

 action of the atmosphere and stand out as ridges on the weathered surface. 

 It was found that in some cases these harder layers were siliceous, while the 

 softer ones were calcareous. In other instances the harder layers were dolo- 

 mitic, and the softer, calcareous, or the harder might be calcareous and the 

 softer argillaceous. At different localities several hundred feet of sediments 

 were found displaying the results of such differential weathering. 



It is somewhat difficult to realize under what conditions these sediments were 

 laid down in order to produce their banded structures. It seems to the writer 

 that these alternating bands, with their different qualities so prominently 

 developed under the influence of weathering, indicate seasonal variations of 

 atmospheric conditions during the period of deposition. That is to say, the 

 harder and more siliceous layers may each represent the amount of sedimen- 

 tation during the annual season of heavy rainfall, when relatively coarse 

 material would be washed down into the inland sea, while the softer layers may 

 represent the product of the dry season when only the finer material would 

 be washed out from the shore.^ 



Thickness. — Allan gives 1,162 feet (354.2 m.) as the total thickness 

 in the Ice River Valley on the east side of Chancellor Peak, and states 

 that there are thicker and better exposed sections on the southwest 

 slope of the Ottertail Valley, and that northwest of Mount Hunter 

 in the Van Horn Range, the Chancellor formation is about 4,500 

 feet (1,371.6 m.) thick.' I examined the Chancellor on the slopes east 



' Loc. cit., p. yj. 

 ^ Idem, pp. 83, 84. 

 ^ Idem, p. 84. 



